Just a word of warning -- that page of schedules hasn't been updated since April 2009.

For the most up to date schedules, here are some links:

By Air
a) Maya Island Air, http://www.mayaregional.com/
b) Tropic Air, http://www.tropicair.com

By Bus
Here's a link to the most up to date schedule for the James Bus Line. Thanks to Ian & Kate at Hickatee Cottages for keeping this up to date:
https://www.hickatee.com/belize_bus_times.html

By Water Taxi
More thanks to Kate & Ian:
https://www.hickatee.com/punta-gorda-water-taxi.html